package/rcw : bump to LSDK-19.09

package/rcw : bump to LSDK-19.09

The new rcw.py script is python3-only, but we can use either the
system-provided python3, or the one we build with host-python3 if
the system does not have it already.

It turns out, also, that rcw.py is using #!/usr/bin/env python3,
so it will easily find it from $PATH, so we export it in the
environment.

Signed-off-by: Laurent Hartanerot <laurent.hartanerot@atos.net>
[yann.morin.1998@free.fr:
  - set the proper PATH in the envioronment
  - do not explicitly call python3, defer to /usr/bin/env in the script
  - add an accompagnying comment
  - rewrite commit log accordingly
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>